Class BasicModelBE

Limiting form of the Bose-Einstein model. The formula used in Lucene differs
slightly from the one in the original paper: F is increased by tfn+1
and N is increased by F

WARNING: This API is experimental and might change in incompatible ways in the next release.

NOTE: in some corner cases this model may give poor performance with Normalizations that
return large values for tfn such as NormalizationH3. Consider using the
geometric approximation (BasicModelG) instead, which provides the same relevance
but with less practical problems.